On Sun, Feb 11, 2018 at 9:29 PM, Ulf Magnusson <ulfalizer@xxxxxxxxx> wrote: > On Sun, Feb 11, 2018 at 6:56 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote: >> Another case I mentioned before that I just want to make sure we don't >> reintroduce the problem of getting "stuck" with a bad .config file. >> While adding _STRONG support, I discovered the two-phase Kconfig >> resolution that happens during the build. If you selected _STRONG with >> a strong-capable compiler, everything was fine. If you then tried to >> build with an older compiler, you'd get stuck since _STRONG wasn't >> support (as detected during the first Kconfig phase) so the >> generated/autoconf.h would never get updated with the newly selected >> _REGULAR). I moved the Makefile analysis of available stack-protector >> options into the second phase (i.e. after all the Kconfig runs), and >> that worked to both unstick such configs and provide a clear message >> early in the build about what wasn't available. >> >> If all this detection is getting moved up into Kconfig, I'm worried >> we'll end up in this state again. If the answer is "you have to delete >> autoconf.h if you change compilers", then that's fine, but it sure >> seems unfriendly. :) > > Did you mean include/config/auto.conf? That's the one that gets > included by the Makefiles. > > If the feature detection is moved into Kconfig, you should only need > to rerun the configuration (make menuconfig/oldconfig/olddefconfig) if > you change the compiler. That will update .config while taking the new > features into account, and then the second phase during 'make' will > update include/config/auto.conf from .config. > > That second Kconfig phase generates include/generated/autoconf.h and > include/config/. The include/config/ directory implements dependencies > between source files and Kconfig symbols by turning the symbols into > (empty) files. When building (during the "second phase"), Kconfig > compares .config with include/config/auto.conf to see what changed, > and signals the changes to 'make' by touch'ing the files corresponding > to the changed symbols. The idea is to avoid having to do a full > rebuild whenever the configuration is changed. > > Check out scripts/basic/fixdep.c as well if you want to understand how it works. > > Cheers, > Ulf By the way: That second phase is also a "normal" Kconfig run in the sense that it does all the usual dependency checking stuff. Even if .config doesn't respect dependencies, include/config/auto.conf will. So I think you might not even need to rerun the configuration (though .config will be out-of-date until you do). Cheers, Ulf -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
